package com.wenhao.newcode.iqiyi;

import java.math.BigDecimal;
import java.math.RoundingMode;

import java.util.Scanner;

/**
 * @author Wenhao Tong
 * @create 2021-08-01 14:57
 */
public class Main1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();
        int k = Integer.parseInt(input.substring(input.lastIndexOf(':') + 1));
        String nums = input.substring(0,input.lastIndexOf(':'));
        String[] array = nums.split(",");
        int[] arr = new int[array.length];
        for (int i = 0;i < arr.length;i++) {
            arr[i] = Integer.parseInt(array[i]);
        }
        double sum = 0;
        int i = 0;
        while (i < k) {
            sum += arr[i];
            i++;
        }
        double change;
        double max = 0;
        Double temp;
        while (i < arr.length) {
            temp = sum - arr[i - k] + arr[i];
            change = (temp - sum) / sum;
            sum = temp;
            max = change > max ? change : max;
            i++;
        }
        BigDecimal b = new BigDecimal(max * 100);
        BigDecimal result = b.setScale(2, RoundingMode.HALF_UP);
        System.out.println(result + "%");
    }
}
